The multi-object mode of GMOS offers the possibility of obtaining spectra of several hundred objects simultaneously. The GMOS MOS design is based upon precisely fabricating and locating a plate containing many small slits within the spectrograph's entrance aperture. With a 5.5 arcmin field of view, 30-60 slits can typically be located in a single mask, with a maximum of several hundred slits when narrow-band filters are used. A total of 18 masks (plus the IFU) can be loaded into GMOS at any given time. Actual mask production is done with a laser milling machine located in Hilo. Currently this laser milling machine produces masks for both GMOSs at Gemini North and Gemini South.

Currently offered capabilities:

• Slit widths 0.5 arcsec or larger
• Masks designed from GMOS direct imaging
• Masks designed from object catalogs

See information about:

• Mask preparation
• Mask design
• Mask-making software
• Checking your mask design
• Mask deadlines (linked from the Phase II instructions for the current semester)
• Observing strategies